There is no provision in the Rules of English Billiards to call a game off, and neither should there be.
Billiards, Sec. 4 The Players: In the time wasting Rule, if the Referee considers that a player is taking an abnormal amount of time over a stroke or the selection of a stroke, he shall warn the player that he is liable to have the game awarded to his opponent. (Note): Players have been known to slow their usual game down in order to try to protect a small lead, which should not be allowed.
In the question posed, the Referee has no right to stop the game or warn the players that he may do so. Whether the game is of the timed format, or of the points version (i.e.) 150 up makes no difference. For a Referee to take this action would be a gross abuse of power and totally wrong.
The Referee while applying the Rules must always remember that the game belongs to the players, who generally do not all play at the same pace.
This question has been answered by Mr Cliff Hazelton, member of the IBSF Referees & Rules Committee.